I am a new user of Channels and almost abandoned the app when I saw some very distracting pixelisation in dark scenes.

I did a bit of reading on these forums and learned that this is a problem with viewing SDR material (UK FreeView) on 4K HDR TVs (Sony KD-55XE7002, in my case).

I tried using the “SDR Mode Switching” option in settings, but discovered two problems.

Neither of the two options “stick”. Both “On App Launch” and “When Playing Video” revert to HDR, at least some of the time, after quitting the Channels app and restarting the AppleTV.

While testing the above problem, I began to realise that the SDR option just doesn’t look right. It does get rid of the pixelisation issue, but it’s too dark and lacks clarity. The same SDR source looks much better (pixelisation aside) in Channels under HDR than SDR. Even the Chanels Settings screen looks wrong in SDR mode. If I could screenshot my AppleTV I could illustrate this, it’s very easy to see.

I switched off HDR/SDR mode switching in Channels a while back because I found the switching unreliable as well. I just run my ATV in SDR mode by default. Channels looks fine, and the ATV switches automatically to HDR mode when it needs to for other apps/content.

I did the same as @stoli412. My ATV runs in SDR mode. My TV looks much better in SDR mode for SDR sources including Channels. HDR sources just about look as good in HDR mode as in SDR mode - the TV HDR is that sucky. I don’t get any pixelation in any mode though. I do with the Fire TV 1 but that is specific to that model’s hardware not Channels.

I think most visual issues people are having will be down to the TV not the Apple TV.

I’ve done some more experimentation since starting this thread and have to admit my second complaint was a red herring. It turns out my TV has an HDR “scene” setting that is automatically invoked when it recognises HDR input (from the Apple TV) but which is not changed when Channels switches to SDR. Manually changing the scene to “Auto” (or anything other than “HDR”) eliminates any visual unpleasantness.

My first issue still stands, though. Channels does not work as expected with either SDR option selected. After Channels has been force quit and the Apple TV restarted, Channels will return to HDR mode despite Settings indicating that SDR should be in effect.

So I’m starting to wonder if there are deeper issues going on with SDR/HDR mode switching in Channels. As I said earlier, I have my ATV set to 4K SDR 50Hz, and I have Channels colour mode switching set to Off. Out of curiosity, I set mode switching to On (video player, not app start) in Channels but made no changes to the ATV settings. Unexpectedly, when I tune to a channel, my TV goes black for a few seconds like it does when the ATV changes colour modes or frame rates, even though no changes should have been required. Any idea why it would do this?

I was testing partly because of this thread but also because I’ve been experiencing even more issues with Channels since tvOS 11.3 was released. In addition to the occasional jerky picture I’ve previously reported (Judder issue after skipping adverts?), I’ve also been getting random picture dropouts where in goes black for a split second. Again, only seeing this issue in Channels.

Now, a few things have updated recently: the tvOS 11.3 update, but also a firmware update to my TV (Sony KD-55XE9305) to finally enable Dolby Vision. Even though I’m only seeing issues in Channels, I thought I’d try replacing my HDMI cables to see if the problems resolve. I replaced them with ‘premium certified’ HDMI cables but saw no changes in behaviour.

That lead me to continue experimenting with ATV and Channels settings. I decided to change the ATV to output 4K Dolby Vision 50 Hz by default, and I changed Channels back to no mode switching (meaning Channels would be output in HDR/Dolby Vision). Surprisingly, no more judder and no more split-second picture dropouts! Any reason why that would be? Is it possible that with my original config (ATV SDR default, Channels mode switching off) Channels is still doing something to the video output that’s causing issues with my TV?

Even though the issues appear to be resolved if setting the ATV to HDR/DV by default, it’s not the ideal setup for me as I still find the ATV SDR—>HDR tone mapping to be not quite right. (It’s got much better but still not there for daily use in my opinion, not to mention the increased energy use when always running in HDR.)

I’ve tested both options, and neither work reliably. I prefer not to use the “when playing video” option, as it causes the TV to switch modes too often, which is quite distracting. Preferred behaviour would be to switch to SDR when launching the app. This currently does not happen, regardless of which setting is selected.

I’m still having the problem described above — “SDR Mode Switching” does not work as expected between Channels app launches. The setting is remembered (as in, the trick remains beside “On app launch”, but the switch is not made — I have to manually select “On app launch” to trigger it.

I think, nearly two years later and having experienced exactly the same behavior consistently on two AppleTVs and two TV sets, that this is linked to my habit of quitting/launching the Channels app while in the guide (or any menu) rather than while video is playing.

If "SDR Mode Switching" is set to "On app launch" but Channels.app launches into the guide — because that's the state it was in when last quit — the setting is not triggered.

Is there a way to ensure "SDR Mode Switching" is triggered in these circumstances?

What if you set the AppleTV to 4K SDR and turn on match range and framerate in ATV settings. Then try playing something 4K HDR, like from Amazon or Netflix. And see if the mode switches. If it does, then you have a solution. Keep SDR on in the ATV and all SDR apps work in native dynamic range. And then when you go to play something HDR, it will switch automatically.